Syntheses, structures, and magnetic properties of Np3S5 and Np3Se5

Black prisms of Np(3)Q(5) (Q = S, Se) have been synthesized by the stoichiometric reactions between Np and Q at 1173 K in a CsCl flux. The structures of these compounds were characterized by single-crystal X-ray diffraction methods. The Np(3)Q(5) compounds are isostructural with U(3)Q(5). The structure of Np(3)Q(5) is constructed from layers of Np(1)Q(8) distorted bicapped trigonal prisms that share faces with each other on bc planes. Each Np(1)Q(8) layer further shares Q(2) edges with two adjacent identical neighbors to form a three-dimensional framework. The space inside each channel within this framework is filled by one single edge-sharing Np(2)Q(7) distorted 7-octahedron chain running along the b axis. Magnetic susceptibility measurements show that Np(3)S(5) and Np(3)Se(5) have antiferromagnetic orderings at 35(1) and 36(1) K, respectively. Above the magnetic ordering temperatures, both Np(3)S(5) and Np(3)Se(5) behave as typical Curie-Weiss paramagnets. The effective moments obtained from the fit of the magnetic data to a modified Curie-Weiss law over the temperature range 70 to 300 K are 2.7(2) μ(B) (Np(3)S(5)) and 2.9(2) μ(B) (Np(3)Se(5)).     

Crystallization kinetics of amorphous S20Se80

The effect of temperature on the crystallization kinetics of bulk amorphous S₂₀Se₈₀ has been studied using differential scanning calorimetry. Using the empricial Avrami expressions, a number of kinetic parameters has been determined. The order of the reactionn was found to be 2.3 for the range of temperature 340–365 K and 1.6 in the range of temperature between 370–400 K. This range ofn indicates that the crystallization process is diffusion controlled growth with decreasing nucleation rate. The activation energy was found to be 3, 1.1 ev depending on the same range of temperatures.A time-temperature-transformation (TTT) curves has been plotted from isothermal results over the temperature range 340 K to 400 K showing the presence of minimum at 374 K. From theTTT curves the critical cooling rate required to avoid 25, 50, 75 and 100% crystallization was found to be 2.4, 1.79, 0.72 and 0.42C/sec respectively.

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Zusammenfassung Mittels DSC wurde der Einflu\ der Temperatur auf die Kristallisierungskinetik von amorphem S₂₀Se₈₀ untersucht. Unter Verwendung der empirischen Avrami Gleichungen wurde eine Anzahl kinetischer Grö\en ermittelt. Danach ergab sich die Reaktionsordnung n für den Temperaturbereich 340–365 K mit 2.3 und für den Temperaturbereich 370–400 K mit 1.6. Dieses Intervall fürn zeigt, da\ es sich beim Kristallisationsproze\ um ein diffusionsbestimmtes Wachstum mit sinkender Kristallkeimbildungsgeschwindigkeit handelt. Für die Aktivierungsenergie wurde für die gleichen Temperaturbereiche ein Wert von 3 bzw. 1.1 eV gefunden.Ausgehend von den isothermen Ergebnissen im Temperaturbereich 340–400 K wurde eine Zeit-Temperatur-Transformationskurve (TTT) dargestellt, die bei 374 K die Gegenwart eines Minimum aufweist. Auf der Basis derTTT-Kurven konnte für eine 25-, 50-, 75-bzw. 100-prozentige Kristallisation eine kritische Kühlgeschwindigkeit von 2.4, 1.79, 0.72 bzw. 0.42C/s ermittelt werden.

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The author wish to thank Prof. Dr. M.F. Kotkata Department of Physics, at Ain Shams University in Cairo, for his valuable discussions, and also Dr. F. Sale the head of the Metallurgy department at UMIST in Manchester. Who gave the facility of doing the experimental work in his department.     

Ultraviolet photoelectron studies of the molecules Se5, Se6, Se7 and Se8 with relevance to their geometrical structure

The vacuum-UV-photoelectron spectra (hν=10.0 eV) of Se₂, Se₅, Se₆, Se₇ and Se₈ were measured. The isolated particles were examined in a supersonic molecular beam employing the photoelectron-photocation-coincidence technique. The structures of the photoelectron spectra of selenium molecules with even and odd numbers of atoms differ in a characteristic manner. Whereas the spectra of Se₆ and Se₈ show one single broad band, three separated bands with different intensities are observed for Se₅ and two for Se₇. An attempt to connect these experimental observations with the geometrical structure of the molecules shows that the photoelectron spectra are consistent with theC _1h -symmetry of the Se₅ and Se₇ rings proposed in the literature.     

Ring currents as probes of the aromaticity of inorganic monocycles : P5-, As5-, S2N2, S3N3-, S4N3+, S4N42+, S5N5+, S42+ and Se42+

Current-density maps were calculated by the ipsocentric CTOCD-DZ/6-311G** (CTOCD-DZ=continuous transformation of origin of current density-diamagnetic zero) approach for three sets of inorganic monocycles: S(4) (2+), Se(4) (2+), S(2)N(2), P(5) (-) and As(5) (-) with 6 pi electrons; S(3)N(3) (-), S(4)N(3) (+) and S(4)N(4) (2+) with 10 pi electrons; and S(5)N(5) (+) with 14 pi electrons. Ipsocentric orbital analysis was used to partition the currents into contributions from small groups of active electrons and to interpret the contributions in terms of symmetry- and energy-based selection rules. All nine systems were found to support diatropic pi currents, reinforced by sigma circulations in P(5) (-), As(5) (-), S(3)N(3) (-), S(4)N(3) (+), S(4)N(4) (2+) and S(5)N(5) (+), but opposed by them in S(4) (2+), Se(4) (2+) and S(2)N(2). The opposition of pi and sigma effects in the four-membered rings is compatible with height profiles of calculated NICS (nucleus-independent chemical shifts).     

Reciprocal system 3Tl2S + Bi2Se3 ↔ 3Tl2Se + Bi2S3

The reciprocal system 3Tl₂S + Bi₂Se₃ ? 3Tl₂Se + Bi₂S₃ has been investigated by DTA, X-ray powder diffraction analysis, and emf measurements. Some polythermal sections and the isothermal section at 500 K of the phase diagram and the projection of the liquidus surface of this system have been constructed, and the types and coordinates of the invariant and univariant equilibria have been determined. The existence of wide regions of quaternary solid solutions based on the binary compounds Tl₂S, Tl₂Se, Bi₂S₃, and Bi₂Se₃, and solid solutions between the temary compounds TlBiS₂ and TlBiSe₂ have been established.     

Schichtanionen in den Kristallstrukturen der isotypen Verbindungen Sr2[Ga2S5], Ba2[In2S5] und Ba2[In2Se5]

Layer-Anions in the Crystal Structures of the Isotypic Compounds Sr₂[Ga₂S₅], Ba₂[In₂S₃], and Ba₂[In₂Se₅] The compounds Sr₂[Ga₂S₅], Ba₂[In₂S₅], and Ba₂[In₂Se₅] have been prepared from stoichiometric mixtures of the elements at temperatures between 1150°C and 1250°C. They are isotypic (space group Pbca, Z = 8) with the lattice constants see ?Inhaltsübersicht”?. In the anionic part of the structure GaS₄-(InS₄-/InSe₄)-tetrahedra share three common vertices to form layers with rings built by four and eight tetrahedra. The cations are placed between the sheets and have the coordination number seven.     

Darstellung und Kristallstruktur von RbSb3Se5

Preparation and Crystal Structure of RbSb₃Se₅ RbSb₃Se₅ was prepared by methanolothermal reaction of Rb₂CO₃ with Sb₂Se₃ at a temperature of 175°C. An X-ray structural analysis demonstrated that the compound contains polyselenoantimonate(III) anions (Sb₃Se₅^?)_n. A ψ-tetrahedral coordination is observed for one of the independent Sb atoms, a ψ-trigonal bipyramidal coordination for the other two. The Sb? Se polyhedra are linked through joint edges into sheets.     

Darstellung und Kristallstruktur der Dialkalimetalltrichalkogenide Rb2S3, Rb2Se3, Cs2S3 und Cs2Se3

Preparation and Crystal Structure of the Dialkali Metal Trichalcogenides Rb₂S₃, Rb₂Se₃, Cs₂S₃, and Cs₂Se₃ Crystalline products were obtained by the reaction of the pure alkali metals with the chalcogens in the molar ratio 2:3 in liquid ammonia at pressures up to 3000 bar and temperatures around 600 K. The substances crystallize in the K₂S₃ type structure (space group Cmc2₁(NO. 36)). Unit cell constants see ?Inhaltsübersicht”?. The characteristic feature of this structure are bent polyanions X₃^2?:(X = S,Se). The new described compounds are compared with the other known alkali metal trichalcogenides.     

Force-field calculations for S,Se, and Te hexafluorides

Catalysis Institute, Siberian Branch, USSR Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 1, pp. 50–54, January–February, 1989.     

Radiation stability of methionine-35S and selenomethionine-75Se

The radiation stability of methionine-³⁵S and selenomethionine⁷⁵Se was investigated using the methods of thin-layer chromatography, gas chromatography and ESR. Radiation decomposition of methionine-³⁵S mainly consists in an oxidation process and in the release of volatile products. The ESR-spectra of irradiated DL-methionine indicated a strong localization of the unpaired electrons on sulfur atoms. Radiation damage to selenomethionine-⁷⁵Se as a function of radiation dose proved an increased stability of this compound, and its radiation decomposition consists in the formation of oxidized products and by direct rupture of the selenium bonds accompanied by the formation of volatile compounds like CH₃SeH and SeH₂. The self-radiolysis of the aqueous solution of selenomethionine-⁷⁵Se during its storage in air leads, however, to a lower decomposition rate which consists in the release of inorganic selenium and in an oxidation process.     

Crystal structure of diselenium pentoxide Se2O5

The structure of monoclinic Se₂O₅, S. G. P2₁/c, Z = 4, was solved by direct methods and refined by an anisotropic full matrix least-squares to R = 0.116 for 855 densitometer intensities. The structure consists of zig-zag chaines [? Se(O)? O? Se(O)₂? O? ]_n with alternating Se(IV) and Se(VI) atoms. Each Se atom is coordinated tetrahedrally, Se(VI) by 4 O atoms, Se(IV) by 3 O atoms and a lone electron pair.